Battery pack

ABSTRACT

A battery pack includes: battery cells, each including end portions in a height direction; a case accommodating the battery cells and a cooling fluid; and first and second holder plates coupled to the case to face each other along the case such that the end portions of the battery cells are insertable therethrough, an accommodation space being defined between the first and second holder plates, and heights of the case, the battery cells, and the first and second holder plates in the height direction satisfy the following condition: a height between the first and second holder plates &lt;a height of the battery cells &lt;a height of the case, and the case includes a hollow member which is open in the height direction.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of Korean Patent Application No.10-2019-0111553, filed on Sep. 9, 2019 in the Korean IntellectualProperty Office, the entire disclosure of which is incorporated hereinby reference.

BACKGROUND 1. Field

Aspects of one or more embodiments relate to a battery pack.

2. Description of the Related Art

In general, secondary batteries refer to batteries that may be chargedand recharged, unlike non-rechargeable primary batteries. Secondarybatteries are used as energy sources of devices, such as mobile devices,electric vehicles, hybrid electric vehicles, electric bicycles, anduninterruptible power supplies. Single-cell secondary batteries ormulti-cell secondary batteries (secondary battery packs) in which aplurality of battery cells are connected as one unit are used accordingto the types of external devices that use the secondary batteries.

Small mobile devices, such as cellular phones, may be operated for acertain time (e.g., a predetermined time) using single-cell secondarybatteries. However, multi-cell secondary batteries (secondary batterypacks) having high-output, high-capacity features may be suitable fordevices having long operating times and requiring high power, such aselectric vehicles or hybrid electric vehicles consuming large amounts ofpower. The output voltage or current of a battery pack may be increasedby adjusting the number of batteries (battery cells) included in thebattery pack.

SUMMARY

According to an aspect of one or more embodiments, a battery pack havingan accommodation space in which a flow of a cooling fluid is induced fordirect contact with battery cells, thereby improving heat dissipationefficiency, is provided.

According to another aspect of one or more embodiments, a battery packin which a cooling fluid is insulated to prevent or substantiallyprevent electrical interference between the cooling fluid and electrodesof battery cells is provided.

Additional aspects will be set forth, in part, in the description whichfollows and, in part, will be apparent from the description, or may belearned by practice of the presented embodiments of the disclosure.

According to one or more embodiments, a battery pack includes: batterycells, each including end portions in a height direction of the batterycells; a case accommodating the battery cells and a cooling fluid tocool the battery cells; and a first holder plate and a second holderplate that are coupled to the case to face each other along the casesuch that the end portions of the battery cells are insertable throughthe first and second holder plates, an accommodation space being definedbetween the first and second holder plates to accommodate the coolingfluid, wherein the case, the battery cells, and the first and secondholder plates have heights in the height direction of the battery cellsthat satisfy the following condition: a height between the first andsecond holder plates <a height of the battery cells <a height of thecase, and the case includes a hollow member which is open in the heightdirection.

In one or more embodiments, assembling protrusions may protrude outwardfrom the first and second holder plates away from the accommodationspace and may hold the end portions of the battery cells.

In one or more embodiments, the first and second holder plates mayinclude cell holes, and the battery cells may be insertable into thecell holes, and the assembling protrusions may be arranged along rows ofthe cell holes to hold the end portions of the battery cells neighboringeach other in a state in which the assembling protrusions are atpositions between the cell holes neighboring each other.

In one or more embodiments, the battery pack may further include a busbar electrically connecting the battery cells to each other, whereinsome of the assembling protrusions may include first assemblingprotrusions that hold the end portions of the battery cells and do notphysically interfere with the bus bar, and others of the assemblingprotrusions may include second assembling protrusions that hold the endportions of the battery cells and the bus bar.

In one or more embodiments, the bus bar may include a main bodyextending along rows of the battery cells and branches branching fromthe main body toward the battery cells, and the branches and theassembling protrusions may be staggered in a zigzag pattern centered onthe main body.

In one or more embodiments, the main body may extend in a row directionof the battery cells between outermost branches located on ends of themain body, and the second assembling protrusions may be adjacent toinner sides of the outermost branches.

In one or more embodiments, the first and second assembling protrusionsmay include first protrusion portions protruding toward the end portionsof the battery cells, and the second assembling protrusions may furtherinclude second protrusion portions protruding toward the bus bar.

In one or more embodiments, the first protrusion portions may be onopposite sides of the second assembling protrusions, and the secondprotrusion portions may be on sides of the second assembling protrusionsbetween the opposite sides.

In one or more embodiments, the first and second protrusion portions mayhave a height difference in the height direction.

In one or more embodiments, cell ribs may protrude inward from the firstand second holder plates toward the accommodation space and may bearranged around outer circumferential surfaces of the battery cells.

In one or more embodiments, gaps may be defined between the outercircumferential surfaces of the battery cells and the cell ribs.

In one or more embodiments, the case may include outer walls and innerwalls extending in parallel to each other along edges of the case whichsurround the accommodation space.

In one or more embodiments, the battery cells, the outer walls, and theinner walls may have heights that satisfy the following condition: aheight of the inner walls <the height of the battery cells <a height ofthe outer walls.

In one or more embodiments, well spaces may be defined between the outerwalls and the inner walls along the edges of the case.

In one or more embodiments, the battery pack may further include apotting resin on the first and second holder plates, and the pottingresin may be continuously provided in the well spaces.

In one or more embodiments, skirt portions may be bent inward from thefirst and second holder plates toward the well spaces and may beinserted into the well spaces.

In one or more embodiments, the skirt portions may be bent and extendfrom the first and second holder plates and may be arranged around theinner walls.

In one or more embodiments, the battery pack may further include apotting resin on the first and second holder plates.

In one or more embodiments, the potting resin on the first and secondholder plates may have a height in the height direction that satisfiesthe condition: the height of the battery cells <a height of the pottingresin <the height of the case.

In one or more embodiments, the battery pack may further include a busbar electrically connecting the battery cells to each other, wherein thepotting resin may cover coupling portions between the bus bar and thebattery cells.

In one or more embodiments, the potting resin on the first and secondholder plates may have a height in the height direction that satisfiesthe following condition: the height between the first and second holderplates <the height of the potting resin <the height of the batterycells.

In one or more embodiments, the potting resin may expose vents in theend portions of the battery cells.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of certainembodiments of the disclosure will be more apparent from the followingdescription, taken in conjunction with the accompanying drawings, inwhich:

FIGS. 1 and 2 are exploded perspective views illustrating a battery packaccording to an embodiment;

FIG. 3 is a cutaway perspective view illustrating the battery pack shownin FIG. 1;

FIG. 4 is a cross-sectional view illustrating the battery pack shown inFIG. 3;

FIG. 5 is a plan view illustrating the battery pack shown in FIG. 1;

FIG. 6 is an enlarged perspective view illustrating a portion of thebattery pack shown in FIG. 1;

FIG. 7 is view illustrating a manner in which first and second holderplates and a case shown in FIG. 3 are coupled and assembled together;

FIG. 8 is a cutaway perspective view illustrating filling of a pottingresin in the battery pack according to an embodiment;

FIGS. 9A and 9B are a cross-sectional view illustrating the battery packshown in FIG. 8, and an enlarged cross-sectional view illustrating aportion of the battery pack shown in FIG. 9A, respectively.

FIG. 10 is an enlarged cross-sectional view illustrating a region “X” inFIG. 9A;

FIG. 11 is a cutaway perspective view illustrating filling of a pottingresin in a battery pack according to another embodiment;

FIGS. 12A and 12B are a cross-sectional view illustrating the batterypack shown in FIG. 11, and an enlarged cross-sectional view illustratinga portion of the battery pack shown in FIG. 12A, respectively;

FIG. 13 is a partially exploded perspective view illustrating a covercoupled to the battery pack shown in FIG. 11; and

FIGS. 14 and 15 are an exploded perspective view and a plan view,respectively, which illustrate a partition wall structure of the batterypack according to an embodiment.

DETAILED DESCRIPTION

Reference will now be made in further detail to some embodiments,examples of which are illustrated in the accompanying drawings, whereinlike reference numerals refer to like elements throughout. In thisregard, the present embodiments may have different forms and should notbe construed as being limited to the descriptions set forth herein.Accordingly, the embodiments are merely described below, by referring tothe figures, to explain aspects of the present description. As usedherein, the term “and/or” includes any and all combinations of one ormore of the associated listed items. Throughout the disclosure, theexpression “at least one of a, b, or c” indicates only a, only b, onlyc, both a and b, both a and c, both b and c, all of a, b, and c, orvariations thereof.

It is to be understood that, although the terms “first,” “second,” etc.may be used herein to describe various components, these componentsshould not be limited by these terms. These terms are used todistinguish one component from another.

As used herein, the singular forms “a,” “an,” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise.

It is to be understood that the terms “comprise,” “include,” and “have”used herein specify the presence of stated features or components, butdo not preclude the presence or addition of one or more other featuresor components.

Sizes of components in the drawings may be exaggerated for convenienceof description. In other words, since the sizes and thicknesses ofcomponents in the drawings may be arbitrarily illustrated forconvenience of description, the following embodiments are not limitedthereto.

When a certain embodiment may be implemented differently, a particularprocess order may be performed differently from the described order. Forexample, two consecutively described processes may be performedsubstantially at the same time or performed in an order opposite to thedescribed order.

It is to be understood that when a layer, region, or component isreferred to as being “connected to” another layer, region, or component,it may be directly connected to the other layer, region, or component ormay be indirectly connected to the other layer, region, or componentwith one or more intervening layers, regions, or components interposedtherebetween. For example, it is to be understood that when a layer,region, or component is referred to as being “electrically connected to”another layer, region, or component, it may be directly electricallyconnected to the other layer, region, or component or may be indirectlyelectrically connected to the other layer, region, or component with oneor more intervening layers, regions, or components interposedtherebetween.

Spatially relative terms, such as “beneath,” “below,” “lower,” “above,”“upper,” and the like, may be used herein for ease of description todescribe one element or feature's relationship to another element(s) orfeature(s) as illustrated in the figures. It is to be understood thatthe spatially relative terms are intended to encompass differentorientations of the device in use or operation in addition to theorientation depicted in the figures. For example, if the device in thefigures is turned over, elements described as “below” or “beneath” otherelements or features would then be oriented “above” the other elementsor features. Thus, the exemplary term “below” can encompass both anorientation of above and below. The device may be otherwise oriented(rotated 90 degrees or at other orientations) and the spatially relativedescriptors used herein interpreted accordingly.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which example embodiments of theinventive concept belong. It is to be further understood that terms,such as those defined in commonly-used dictionaries, should beinterpreted as having a meaning that is consistent with their meaning inthe context of the relevant art and will not be interpreted in anidealized or overly formal sense unless expressly so defined herein.

Battery packs will now be described according to some exampleembodiments with reference to the accompanying drawings.

FIGS. 1 and 2 are exploded perspective views illustrating a battery packaccording to an embodiment; FIG. 3 is a cutaway perspective viewillustrating the battery pack shown in FIG. 1; FIG. 4 is across-sectional view illustrating the battery pack shown in FIG. 3; FIG.5 is a plan view illustrating the battery pack shown in FIG. 1; and FIG.6 is an enlarged perspective view illustrating a portion of the batterypack shown in FIG. 1.

Referring to FIGS. 1 and 2 together, a battery pack according to anembodiment may include: a plurality of battery cells 10; a case 100accommodating the battery cells 10 and a cooling fluid for cooling thebattery cells 10; and first and second holder plates 110 and 120assembled to the case 100 to face each other along the case 100 suchthat first and second end portions 11 and 12 of the battery cells 10 maybe inserted through the first and second holder plates 110 and 120, andan accommodation space G1 (refer to FIG. 2) for containing the coolingfluid therein may be formed between the first and second holder plates110 and 120.

In an embodiment, each of the battery cells 10 may be a cylinder-typebattery cell which has a first end portion 11 and a second end portion12 in a height direction thereof, and a cylindrical outercircumferential surface 15 between the first and second end portions 11and 12. In the present specification, the height direction may refer tothe length direction of the battery cells 10. For example, in thepresent specification, the height direction of the case 100 may be thesame as the height direction of the battery cells 10.

In an embodiment, the first and second end portions 11 and 12, which areopposite each other in the height direction of the battery cells 10, maycorrespond to electrodes which have different polarities and throughwhich charge or discharge current is input or output. For example, thefirst and second end portions 11 and 12 may respectively include upperelectrodes and lower electrodes of the battery cells 10 in the heightdirection. In this case, the first and second end portions 11 and 12 aredefined according to upper and lower positions in the height directionrather than according to polarities, that is, positive and negativepolarities. Thus, some of the first end portions 11 of the battery cells10 may have a positive polarity, and the others of the first endportions 11 of the battery cells 10 may have a negative polarity.Similarly, some of the second end portions 12 of the battery cells 10may have a positive polarity, and the others of the second end portions12 of the battery cells 10 may have a negative polarity. For example,the battery cells 10 may be overturned relative to each other in theheight direction such that the polarities of the first and second endportions 11 and 12 of the battery cells 10 in two neighboring rows maybe reversed. That is, the first and second end portions 11 and 12 mayhave different polarities in this manner, and, as described later, thefirst and second end portions 11 and 12 of the battery cells 10 in twoneighboring rows may be electrically connected to each other using busbars B to connect different polarities of the battery cells 10 in seriesin the two neighboring rows. In this case, the first and second endportions 11 and 12 of the battery cells 10 in the same row may beconnected in parallel by connecting end portions having the samepolarity through bus bars B, and the first and second end portions 11and 12 of battery cells 10 in neighboring rows may be connected inseries by connecting end portions having different polarities throughbus bars B.

In another embodiment, electrodes having different polarities throughwhich charge and discharge current is input or output may be formed onend portions selected from the first and second end portions 11 and 12,which are opposite in the height direction of the battery cells 10, and,in this case, different portions of the selected end portions may havepositive and negative polarities. Further, in embodiments, the batterycells 10 may be of any type, including a prismatic type, for example,without being limited to a cylinder type. In an embodiment, the batterypack may be mounted on a moving unit, such as a vehicle, to providepower to the moving unit, and, in this case, the battery pack mayinclude a large-capacity battery cell 10 or a plurality oflarge-capacity battery cells 10 to provide required output performance.

Referring to FIG. 1, the battery cells 10 of the battery pack may beelectrically connected to each other through bus bars B. In anembodiment, the bus bars B may include a plurality of bus bars B, eachelectrically connecting two neighboring rows of battery cells 10. Forexample, the bus bars B may include first bus bars B1, each connected tothe first end portions 11 of battery cells 10 included in twoneighboring rows, and second bus bars B2, each connected to the secondend portions 12 of battery cells 10 in the two neighboring rows. Thefirst and second bus bars B1 and B2 may be arranged at upper and loweropposite positions in the height direction of the battery cells 10 so asto be respectively connected to the first and second end portions 11 and12 of the battery cells 10.

Each of the bus bars B may include a main body Ba which extends in thedirection of rows of the battery cells 10, and a plurality of branchesBr which branch off from the main body Ba toward the first and secondend portions 11 and 12 of the battery cells 10. In an embodiment, a busbar B may electrically connect two neighboring rows of battery cells 10,and, in this case, the main body Ba may extend along the two neighboringrows of battery cells 10, and the branches Br may protrude toward thefirst and second end portions 11 and 12 from intermittent positions ofthe main body Ba. In an embodiment, the main body Ba may have both endson the outermost branches Br and may extend between the outermostbranches Br, and may be fixed by assembling protrusions S (correspondingto second assembling protrusions S2), as described later.

Referring to FIG. 1, in an embodiment, a measurement terminal Bt foroutputting voltage information of battery cells 10 may be formed on themain body Ba of a bus bar B, and, according to an embodiment, themeasurement terminal Bt may protrude outward from the main body Ba ofeach bus bar B. In an embodiment, output terminals P may be formed onsome of the bus bars B such that charge and discharge currents may beinput or output through the output terminals P, and, according to anembodiment, the output terminals P may be formed on the outermost secondbus bars B2, which are arranged at outermost positions among second busbars B2.

Referring to FIGS. 2 and 3 together, in an embodiment, the case 100 maybe formed as a hollow member which is open in the height direction toaccommodate the battery cells 10 and the cooling fluid for cooling thebattery cells 10. For example, the case 100 may provide theaccommodation space G1 for accommodating the battery cells 10 and thecooling fluid for cooling the battery cells 10, and inner walls 102 forassembling the first and second holder plates 110 and 120 and outerwalls 101 for confining a potting resin F (described later withreference to FIG. 8) may be formed along edges of the case 100 whichsurround the accommodation space G1. The inner walls 102 and the outerwalls 101 may extend side by side along the edges of the case 100. In anembodiment, the inner walls 102 and the outer walls 101 are connected toeach other through bottom surfaces 103 provided therebetween and mayhave different heights from the bottom surfaces 103. The inner walls 102and the outer walls 101 of the case 100 may form well spaces W (refer toFIG. 3) therebetween, which will be described further later.

The case 100 may provide rigidity to the battery pack and may protectthe battery cells 10 accommodated therein from the outside. For example,in some embodiments, the battery pack may be attached to a moving unit,such as a vehicle, and may have a certain degree of strength in a caseof collision of the moving unit. In an embodiment, the case 100 mayinclude a ductile metal material that has strength and ductility so asnot to be fractured or broken, even when the case 100 is externallyimpacted. For example, if the case 100 includes a brittle material, suchas a plastic or synthetic resin, the case 100 may fracture or break dueto impacts with external objects, and, thus, in an embodiment, the case100 may include a metal material, such as aluminum. In addition, thecase 100 may function as a heat sink for the battery cells 10accommodated therein and the cooling fluid for cooling the battery cells10 and may thus include a metal material, such as aluminum, having highthermal conductivity. As described later, in an embodiment, a pluralityof reinforcing ribs 108 (refer to FIG. 2) are formed along the outerside of the case 100 to supplement the structural rigidity of the case100 and increase the heat dissipation area of the case 100.

In an embodiment, the case 100 may be formed in a substantiallyrectangular parallelepiped shape including a pair of long side portions100L and first and second short side portions 100S1 and 100S2 connectingthe pair of long side portions 100L to each other, and, in anembodiment, the case 100 may be formed in a serpentine shape along theouter circumferential surfaces 15 of the battery cells 10, which arearranged along the edges of the case 100. In this case, since thesurface area of the case 100 having a serpentine shape is increased,heat dissipation may be facilitated, and the case 100 may absorbexternal shocks while the case 100 deforms more flexibly according tothe external shocks. However, in an embodiment, the serpentine shape ofthe case 100 may be formed along the long side portions 100L of the case100, and the first and second short side portions 100S1 and 100S2 of thecase 100 may be flat. In an embodiment, an inlet I and an outlet O maybe formed in the first short side portion 100S1 to allow the coolingfluid to flow into and out of the case 100, and, thus, the first shortside portion 100S1 may be formed in a flat shape for secure fluidicconnection of an opponent part to the inlet I and the outlet O. In anembodiment, the second short side portion 100S2, which is opposite thefirst short side portion 100S1, may be formed in a flat shape to providea reference mounting or assembling plane when the battery pack ismounted on a device, such as a vehicle, and to stably align the mountingposition of the battery pack in such a device without shaking. In anembodiment, the reinforcing ribs 108 (refer to FIG. 2) may be formedalong the outer side of the case 100 to reinforce the strength of thecase 100. For example, the reinforcing ribs 108 may include a pluralityof first reinforcing ribs 108 a extending in parallel with each other atdifferent heights in the height direction of the case 100, and aplurality of second reinforcing ribs 108 b extending across the firstreinforcing ribs 108 a in the height direction of the case 100. Thereinforcing ribs 108 may reinforce the strength of the case 100 andincrease the surface area of the case 100 to provide a larger heatdissipation area.

Referring to FIGS. 2 and 3, the first and second holder plates 110 and120 may be assembled to the case 100 to face each other along the case100 such that the first and second end portions 11 and 12 of the batterycells 10 may be inserted through the first and second holder plates 110and 120, and the accommodation space G1 accommodating the cooling fluidmay be formed between the first and second holder plates 110 and 120. Aplurality of cell holes 115 into which the battery cells 10 are insertedmay be formed in the first and second holder plates 110 and 120. Inaddition, the first and second holder plates 110 and 120 may include:cell ribs R protruding inward from the first and second holder plates110 and 120 to surround the outer circumferential surfaces 15 of thebattery cells 10; and assembling protrusions S protruding outward fromthe first and second holder plates 110 and 120 to hold the first andsecond end portions 11 and 12 of the battery cells 10. The cell holes115, the cell ribs R, and the assembling protrusions S formed on thefirst and second holder plates 110 and 120 will be described furtherlater.

Together with the case 100, the first and second holder plates 110 and120 may form the accommodation space G1 which accommodates the coolingfluid for cooling the battery cells 10. The first and second holderplates 110 and 120 may include inner surfaces which face theaccommodation space G1 of the cooling fluid, and outer surfaces whichare opposite the inner surfaces, and, as described below, a pottingresin F (refer to FIG. 8) may be formed on the outer surfaces of thefirst and second holder plates 110 and 120 to certain heights (e.g.,predetermined heights) to seal the accommodation space G1 of the coolingfluid.

In the present specification, the cooling fluid may refer to a liquidcooling medium having a relatively high thermal capacity and thus arelatively high cooling ability compared to a gaseous cooling medium,such as air, and may encompass an electrically insulative cooling fluidand an electrically conductive cooling fluid.

However, the technical scope of the present disclosure is not limitedthereto, and, in other embodiments, the cooling fluid may include agaseous cooling medium, for example, a gaseous cooling medium, such as arefrigerant gas. In this case, the cooling fluid including a gaseouscooling medium may be accommodated in the accommodation space G1 betweenthe first and second holder plates 110 and 120, and the cooling fluidaccommodated in the accommodation space G1 may be sealed by the pottingresin F (refer to FIG. 8) formed on the outer surfaces of the secondholder plates 110 and 120.

Referring to FIGS. 3 and 4, the first and second holder plates 110 and120 may be assembled to the case 100 to face each other along the case100 and may be located at heights at which the first and second endportions 11 and 12 of the battery cells 10 may be exposed through thefirst and second holder plates 110 and 120, such that the first andsecond end portions 11 and 12 of the battery cells 10 having electricalpolarities may not be in contact with the cooling fluid. In other words,a height HC (refer to FIG. 4) of the battery cells 10 may be greaterthan a height H15 between the first and second holder plates 110 and120, which are assembled to the case 100, and, in this case, the firstand second end portions 11 and 12 of the battery cells 10 may be exposedfrom the accommodation space G1 of the cooling fluid away from the firstand second holder plates 110 and 120. As described later, the height H15between the first and second holder plates 110 and 120 may be regulatedby the inner walls 102 of the case 100 which are in contact with thefirst and second holder plates 110 and 120. Further, in the presentspecification, the height H15 between the first and second holder plates110 and 120 may refer to a height obtained by adding thicknesses t ofthe first and second holder plates 110 and 120 to a height HG of theaccommodation space G1 formed between the first and second holder plates110 and 120. That is, the height H15 between the first and second holderplates 110 and 120 may refer to a height measured between the first andsecond holder plates 110 and 120 without including the assemblingprotrusions S protruding in outward directions from the first and secondholder plates 110 and 120 or the cell ribs R protruding in inwarddirections from the first and second holder plates 110 and 120, and,thus, the thicknesses t of the first and second holder plates 110 and120 may be included in the height H15, but the heights of the assemblingprotrusions S or the cell ribs R may not be included in the height H15.

A height H10 of the case 100 may be greater than at least the height HCof the battery cells 10. The case 100 accommodates the battery cells 10,and, thus, the height H10 of the case 100 may be greater than at leastthe height HC of the battery cells 10 to sufficiently accommodate thebattery cells 10. As described later, the potting resin F may be appliedover the first and second holder plates 110 and 120 to heights coveringthe first and second end portions 11 and 12 exposed through the firstand second holder plates 110 and 120, and, in this case, the height H10of the case 100 serving as a dam for containing the potting resin F maybe greater than at least the height HC of the battery cells 10, suchthat the case 100 may have an additional height remaining even afteraccommodating the potting resin F. In an embodiment, as described above,the height HC of the battery cells 10 is greater than the height H15between the first and second holder plates 110 and 120 assembled to thecase 100, such that the first and second end portions 11 and 12 of thebattery cells 10 may be exposed from the accommodation space G1 of thecooling fluid and protrude from the first and second holder plates 110and 120. That is, the height H15 between the first and second holderplates 110 and 120, the height HC of the battery cells 10, and theheight H10 of the case 100 may satisfy the following condition:H15<HC<H10.

Referring to FIGS. 2 and 3, the cell holes 115 may be formed in thefirst and second holder plates 110 and 120. The battery cells 10 may beinserted into the cell holes 115, and the assembling positions of thebattery cells 10 may be determined according to the arrangement of thecell holes 115. For example, the cell holes 115 may determine theassembling positions of the battery cells 10 adjacent to each other todefine spacings between the battery cells 10. Since spacings between thebattery cells 10 adjacent to each other are ensured, the cooling fluidaccommodated in the accommodation space G1 may flow smoothly along thecircumference of each of the battery cells 10, and, thus, the batterycells 10 may be sufficiently cooled. The cell holes 115 may be formed ina circular shape to surround the outer circumferential surfaces 15 ofthe battery cells 10.

Referring to FIG. 5, the cell holes 115 may be arranged in a pluralityof rows according to the arrangement of the battery cells 10. In thepresent specification, the arrangement of the cell holes 115 may besubstantially the same as the arrangement of the battery cells 10. Forexample, cell holes 115 of adjacent rows may be densely arranged in sucha manner that the cell holes 115 may be staggered and fitted intovalleys between adjacent cell holes 115, while being densely staggeredso as not to form any large empty space between adjacent battery cells10, such as in a matrix pattern arrangement arranged side by side in rowand column directions in a matrix. As described above, since the cellholes 115 of adjacent rows are densely arranged at staggered positions,the battery cells 10 may be compactly arranged, and, thus, the batterypack may have a high energy density relative to a volume of the batterypack.

For reference, in the present specification, the row or column directionmay refer to a direction in which the battery cells 10 are arranged orthe cell holes 115 defining the assembling positions of the batterycells 10 are arranged, and may refer to a direction in which a group ofadjacent battery cells 10 (or cell holes 115) are linearly arranged. Inthe present specification, a direction parallel to the first and secondshort side portions 100S1 and 100S2 may be referred to as the columndirection, and a direction parallel to the long side portions 100L maybe referred to as the row direction. However, embodiments of the presentdisclosure are not limited thereto. For example, the bus bars B (forexample, refer to the main bodies Ba shown in FIG. 1) may extend in thecolumn direction of the battery cells 10 in some embodiments, and mayextend in the row direction of the battery cells 10 in otherembodiments.

Referring to FIGS. 2 and 3, the cell ribs R extending along the cellholes 115 may be formed on the first and second holder plates 110 and120. The cell ribs R may extend inward from the first and second holderplates 110 and 120 and may be arranged around (e.g., surround) the outercircumferential surfaces 15 of the battery cells 10 to stably supportthe battery cells 10. That is, the cell ribs R may extend in the heightdirection of the battery cells 10 to support the battery cells 10 in anupright position with respect to the first and second holder plates 110and 120.

In the present specification, the inward directions of the first andsecond holder plates 110 and 120 may refer to directions in which thefirst and second holder plates 110 and 120 face each other, ordirections in which the first and second holder plates 110 and 120 facethe accommodation space G1 of the cooling fluid which is formed betweenthe first and second holder plates 110 and 120. In addition, the outwarddirections of the first and second holder plates 110 and 120 may referto directions in which the first and second holder plates 110 and 120are spaced apart from each other, or directions in which the first andsecond holder plates 110 and 120 are away from the accommodation spaceG1 of the cooling fluid which is formed between the first and secondholder plates 110 and 120. The inward and outward directions of thefirst and second holder plates 110 and 120 may be parallel with theheight direction of the battery cells 10 and may be opposite each other.

The cell ribs R may protrude inward from the first and second holderplates 110 and 120 toward the accommodation space G1 of the coolingfluid. As described later, the assembling protrusions S which protrudefrom the first and second holder plates 110 and 120 together with thecell ribs R may be outward from the first and second holder plates 110and 120 away from the accommodation space G1 of the cooling fluid. Inthis manner, the cell ribs R and the assembling protrusions S mayprotrude respectively in inward and outward directions of the first andsecond holder plates 110 and 120, that is, in opposite directions fromthe first and second holder plates 110 and 120. For example, the cellribs R may protrude from inner surfaces of the first and second holderplates 110 and 120, and the assembling protrusions S may protrude fromouter surfaces of the first and second holder plates 110 and 120.

In an embodiment, the cell ribs R may protrude in a cylindrical shapefrom the first and second holder plates 110 and 120 to be arrangedaround (e.g., surround) the outer circumferential surfaces 15 of thebattery cells 10. The cell ribs R may protrude from the first and secondholder plates 110 and 120 at positions adjacent to the cell holes 115into which the battery cells 10 are inserted, such that the cell ribs Rmay be arranged around (e.g., surround) the outer circumferentialsurfaces 15 of the battery cells 10. For example, in an embodiment, thecell ribs R may protrude from walls of the first and second holderplates 110 and 120 that are arranged around (e.g., surround) the cellholes 115 into which the battery cells 10 are inserted.

The cell ribs R may protrude from the first and second holder plates 110and 120 in the height direction of the battery cells 10, and, in anembodiment, the protruding length of the cell ribs R may be as short aspossible as long as the cell ribs R stably support the battery cells 10.The cell ribs R are arranged around (e.g., surround) the outercircumferential surfaces 15 of the battery cells 10 while protrudinginward from the first and second holder plates 110 and 120 toward theaccommodation space G1 of the cooling fluid, and, in an embodiment, theprotruding length of the cell ribs R may be short so as not to hinder orblock heat transfer between the cooling fluid and the outercircumferential surfaces 15 of the battery cells 10. For example, thecell ribs R may have a short length so as not to cover center portionsof the battery cells 10 in the height direction of the battery cells 10.In an embodiment, the protruding length of the cell ribs R protrudingfrom the first and second holder plates 110 and 120 in the heightdirection of the battery cells 10 may be about 10 mm when the height HCof the battery cells 10 is about 105 mm. That is, in an embodiment, theprotruding length of the cell ribs R may be about 10% or less of theheight HC of the battery cells 10, for example, about 9.5% of the heightHC of the battery cells 10.

In an embodiment, the cell ribs R may completely surround the outercircumferential surfaces 15 of the battery cells 10. In an embodiment,the cell ribs R may be spaced apart from the outer circumferentialsurfaces 15 of the battery cells 10 by a gap (e.g., a predetermined gap)q (refer to FIG. 3), rather than being in close contact with the outercircumferential surfaces 15 of the battery cells 10, to allow thecooling fluid to make contact with the outer circumferential surfaces 15of the battery cells 10. In an embodiment, for example, the gap q (referto FIG. 3) between the outer circumferential surfaces 15 of the batterycells 10 and the cell ribs R may be about 0.1 mm.

The cooling fluid may make contact with the outer circumferentialsurfaces 15 of the battery cells 10 at a certain flow rate toconvectively transfer heat from the battery cells 10, and, for contactwith the cooling fluid, the gap q (refer to FIG. 3) may be formedbetween the outer circumferential surfaces 15 of the battery cells 10and the cell ribs R.

Referring to FIGS. 3 and 6, the assembling protrusions S may be formedon the first and second holder plates 110 and 120 to hold the first andsecond end portions 11 and 12 of the battery cells 10 for regulating theassembling positions of the battery cells 10 in the height direction.For reference, the cell holes 115 into which the battery cells 10 areinserted may define the assembling positions of the battery cells 10 ina plane in which the battery cells 10 are arranged, and the assemblingprotrusions S may regulate the assembling positions of the battery cells10 in the height direction. The assembling protrusions S may protrudeoutward from the first and second holder plates 110 and 120. That is,the assembling protrusions S may protrude outward from the first andsecond holder plates 110 and 120 in directions opposite the cell ribs R.For example, the assembling protrusions S may protrude from the outersurfaces of the first and second holder plates 110 and 120, and the cellribs R may protrude from the inner surfaces of the first and secondholder plates 110 and 120.

In an embodiment, the assembling protrusions S may protrude from thecircumferences of the cell holes 115 of the first and second holderplates 110 and 120 into which the battery cells 10 are inserted, so asto hold the first and second end portions 11 and 12 of the battery cells10. In an embodiment, two or more assembling protrusions S may be formedon the circumference of each cell hole 115 of the first and secondholder plates 110 and 120 at symmetrical positions to hold edgepositions of each battery cell 10 in a balanced state. In an embodiment,a pair of assembling protrusions S may be formed at opposite positionsalong the circumference of each cell hole 115.

In an embodiment, the assembling protrusions S are formed at positionsbetween neighboring cell holes 115 (or neighboring battery cells 10) inthe rows of the cell holes 115 (or the battery cells 10) such that oneassembling protrusion S may concurrently (e.g., simultaneously) hold twobattery cells 10 inserted into neighboring cell holes 115. However,embodiments of the present disclosure are not limited thereto, and, inother embodiments, the assembling protrusions S may be formed such thatone assembling protrusion S may be among three cell holes 115 havingadjacent circumferences and may thus concurrently (e.g., simultaneously)hold three battery cells 10 inserted into the cell holes 115 adjacent toeach other. In an embodiment, in a structure in which one assemblingprotrusion S is arranged among three cell holes 115 having adjacentcircumferences, a maximum number of assembling protrusions S arrangedbetween one cell hole 115 and six cell holes 115 surrounding the cellhole 115 may be six, and the number of assembling protrusions Ssurrounding one cell hole 115 may be different within a range of six orless according to a design. In addition, the assembling protrusions Ssurrounding one cell hole 115 may be at symmetric or asymmetricpositions.

The assembling protrusions S (outer assembling protrusions S) may alsobe formed on the outer sides of the outermost cell holes 115 (or theoutermost battery cells 10) in the rows of the cell holes 115 (or thebattery cells 10), and each of the outer assembling protrusions S mayhold one battery cell 10. That is, each of inner assembling protrusionsS formed along the rows of the cell holes 115 (or the battery cells 10)may concurrently (e.g., simultaneously) hold two battery cells 10inserted into neighboring cell holes 115, and each of the outerassembling protrusions S formed along the rows of the cell holes 115 (orthe battery cells 10) may hold one battery cell 10 inserted into anoutermost cell hole 115.

Referring to FIG. 6, in an embodiment, each of the inner assemblingprotrusions S formed along the rows of the cell holes 115 (or thebattery cells 10) may include: a center protrusion portion Sc protrudingoutward from the first and second holder plates 110 and 120; and a pairof first protrusion portions Sa branching off from the center protrusionportion Sc toward cell holes 115 (or battery cells 10) located on bothsides. In addition, each of the outer assembling protrusions S formedalong the rows of the cell holes 115 (or the battery cells 10) mayinclude: a center protrusion portion Sc protruding outward from thefirst and second holder plates 110 and 120; and a first protrusionportion Sa protruding from the center protrusion portion Sc toward acell hole 115 (an outermost cell hole 115 or an outermost battery cell10). In an embodiment, the first protrusion portions Sa and the centerprotrusion portions Sc may be formed in a plate shape and may havesubstantially a same width WD.

The assembling protrusions S may protrude outward from the first andsecond holder plates 110 and 120 to hold the first and second endportions 11 and 12 of the battery cells 10 such that the battery cells10 may not be separated from the first and second holder plates 110 and120. For example, the first and second end portions 11 and 12 of thebattery cells 10 may be securely fixed by the assembling protrusions Sprotruding from the first and second holder plates 110 and 120. In anembodiment, for example, the assembling protrusions S may not covervents V formed in the first and second end portions 11 and 12 of thebattery cells 10 so as not to hinder or block the release of internalpressure from the battery cells 10, and may thus protrude only up toclamping portions CL formed on edge portions of the battery cells 10 tophysically interfere with only the clamping portions CL which surroundthe vents V of the battery cells 10.

The assembling protrusions S may hold the first and second end portions11 and 12 of the battery cells 10 at heights to which the assemblingprotrusions S protrude outward from the first and second holder plates110 and 120, thereby fixing the first and second end portions 11 and 12of the battery cells 10 at positions outside the first and second holderplates 110 and 120 and allowing the center portions of the battery cells10 to be exposed to the cooling fluid.

In an embodiment, since the first and second end portions 11 and 12 ofthe battery cells 10 correspond to electrodes to which charge anddischarge currents are input or output, the first and second endportions 11 and 12 of the battery cells 10 are fixed at heights whichare outside the first and second holder plates 110 and 120 forming theaccommodation space G1 of the cooling fluid, thereby insulating thefirst and second end portions 11 and 12 from the cooling fluid.

Some of the assembling protrusions S may hold the first and second endportions 11 and 12 of the battery cells 10 and also hold bus bars Belectrically connected to the battery cells 10. For example, accordingto an embodiment, the assembling protrusion S may include: firstassembling protrusions 51 for holding the first and second end portions11 and 12 of the battery cells 10; and second assembling protrusions S2for holding the first and second end portions 11 and 12 of the batterycells 10 and the bus bars B as well. Hereinafter, the second assemblingprotrusions S2 will be described.

In an embodiment, each of the bus bars B may electrically connect twoneighboring rows of battery cells 10. In this case, the main body Ba ofthe bus bar B may extend between assembling protrusions S arranged intwo rows along the two neighboring rows of battery cells 10. Inaddition, among the assembling protrusions S arranged in two rows withthe main body Ba of the bus bar B therebetween, two assemblingprotrusions S spaced apart from each other may correspond to the secondassembling protrusions S2 which fix the main body Ba of the bus bar B.

The main body Ba of the bus bar B may extend between the outermostbranches Br provided on both ends thereof, and, in this case, the secondassembling protrusions S2 may be assembling protrusions S adjacent tothe outermost branches Br. For example, the second assemblingprotrusions S2 may be assembling protrusions S adjacent to inner sidesof the outermost branches Br, and each of the second assemblingprotrusions S2 may include first protrusion portions Sa for holdingbattery cells 10 and a second protrusion portion Sb for holding the busbar B. In an embodiment, unlike the second assembling protrusions S2,the first assembling protrusions 51, which hold the first and second endportions 11 and 12 of the battery cells 10 without physical interferencewith the bus bars B, may include first protrusion portions Sa but maynot include second protrusion portions Sb.

In an embodiment, the first and second protrusion portions Sa and Sb ofeach of the second assembling protrusions S2 may be centered on thecenter protrusion portion Sc and may protrude in different directionsfrom the center protrusion portion Sc which protrudes outward from thefirst and second holder plates 110 and 120. That is, the firstprotrusion portions Sa may protrude from the center protrusion portionSc in both lateral directions along the rows of the battery cells 10,and the second protrusion portion Sb may protrude from the centerprotrusion portion Sc toward the main body Ba of the bus bar B. In otherwords, each of the second assembling protrusions S2 may include: a pairof first protrusion portions Sa formed on opposite sides of the centerprotrusion portion Sc; and a second protrusion portion Sb protrudingfrom the center protrusion portion Sc between the first protrusionportions Sa. In an embodiment, the first protrusion portions Sa may havesubstantially the same width WD as the center protrusion portion Sc, andthe second protrusion portion Sb may have a width less than the width WDof the first protrusion portions Sa. In this case, the widths of thefirst protrusion portions Sa and the center protrusion portion Sc may bemeasured in the same direction, which is different, for example by 90degrees, from the direction in which the width of the second protrusionportion Sb is measured.

The first and second protrusion portions Sa and Sb are respectivelyconfigured to fix the positions of the first and second end portions 11and 12 of the battery cells 10 and the bus bar B and may have differentstructures which respectively physically interfere with the first andsecond end portions 11 and 12 of the battery cells 10 and the bus bar B.For example, the first protrusion portions Sa may protrude in directionscrossing the first and second end portions 11 and 12 of the batterycells 10 and at a level away from the first and second end portions 11and 12 in the height direction of the battery cells 10, such that thefirst protrusion portions Sa may function as stoppers for the first andsecond end portions 11 and 12 and may hold the first and second endportions 11 and 12 to place the battery cells 10 at designated positionsin the height direction. In an embodiment, the second protrusion portionSb may protrude at the same level as the bus bar B in the heightdirection of the battery cells 10 and may extend in a direction crossingthe bus bar B so as to be inserted into a receiving slot B′ of the busbar B. In an embodiment, the bus bars B may be supported on the firstand second end portions 11 and 12 of the battery cells 10 such thatadditional support structures may not be required for the bus bars B inthe height direction of the battery cells 10, and, for example, as thesecond protrusion portions Sb are fitted into the receive slots B′, thebus bars B may be fixed without movement at a level perpendicular to theheight direction of the battery cells 10.

For example, in each of the second assembling protrusions S2, the firstand second protrusion portions Sa and Sb may protrude from the centerprotrusion portion Sc. In an embodiment, the first protrusion portionsSa may have a small thickness in the height direction of the batterycells 10 and may protrude at a level away from the first and second endportions 11 and 12 of the battery cells 10 in directions crossing thefirst and second end portions 11 and 12, and the second protrusionportion Sb may have a relatively large thickness in the height directionof the battery cells 10 and may be inserted into the receiving slot B′of the bus bar B at the same level as the level of the bus bar B.

In an embodiment, the second protrusion portions Sb may be inserted intothe receiving slots B′ formed in the main body Ba of the bus bar B atdiagonal positions based on the main body Ba of the bus bar B, such thatthe main body Ba of the bus bar B may be supported in a balanced manner.For example, the second protrusion portions Sb may be inserted atdiagonal positions based on the main body Ba of the bus bar B, and,thus, the main body Ba of the bus bar B may be stably supported. Thereceiving slots B′ may be intermittently formed along the main body Baof the bus bar B at diagonally distant positions corresponding to thepositions of the second protrusion portions Sb.

In an embodiment, the second protrusion portions Sb may have a heightdifference in an outward (for example, upward) direction from the firstprotrusion portions Sa. For example, at least outer surfaces (forexample, upper surfaces) of the second protrusion portions Sb may have aheight difference in an outward (for example, upward) direction fromouter surfaces (for example, upper surfaces) of the first protrusionportions Sa in the height direction of the battery cells 10. That is,the second protrusion portions Sb, which hold the main body Ba of thebus bar B, may have a height difference outward (for example, upward)from the first protrusion portions Sa, which hold the first and secondend portions 11 and 12 of the battery cells 10. In an embodiment, themain body Ba of the bus bar B may have a height difference in an outward(for example, upward) direction from the first and second end portions11 and 12 of the battery cells 10 because the branches Br are bent in astepped shape in an inward (for example, downward) direction from themain body Ba (at bent portions Bc) and connected to the first and secondend portions 11 and 12 of the battery cells 10. That is, the secondprotrusion portions Sb, which hold the main body Ba of the bus bar B,may have a height difference outward (for example, upward) from thefirst protrusion portions Sa, which hold the first and second endportions 11 and 12 of the battery cells 10. In an embodiment, thebranches Br of the bus bar B are bent in a stepped shape in an inward(for example, downward) direction from the main body Ba toward the firstand second end portions 11 and 12 of the battery cells 10, such that thebranches Br may be brought into tight contact with the first and secondend portions 11 and 12 of the battery cells 10, and, thus, the weldingstrength between the branches Br and the first and second end portions11 and 12 may be improved.

For example, the second assembling protrusions S2 may fix the positionof the bus bar B (for example, the main body Ba), and, in an embodiment,the bus bar B (for example, the branches Br) is welded to the first andsecond end portions 11 and 12 of the battery cells 10, such that theposition of the bus bar B may be more securely fixed. For example, thebattery cells 10 and the bus bar B may be fixed to each other throughthe second assembling protrusions S2 during welding such that thebattery cells 10 and the bus bar B may be stably welded to each other.

In an embodiment, the branches Br of the bus bar B and the assemblingprotrusions S may be staggered in a zigzag pattern. For example, in anembodiment, each of the bus bars B may electrically connect twoneighboring rows of battery cells 10 to each other. In an embodiment,the two rows of battery cells 10, which are connected to each otherthrough the bus bar B, may be arranged in a zigzag pattern in whichbattery cells 10 in one row are placed in valleys between battery cells10 in the other row. Therefore, the branches Br of the bus bar Bconnected to the first and second end portions 11 and 12 (for example,electrodes formed in center portions of the first and second endportions 11 and 12) of the battery cells 10 may be arranged in a zigzagpattern centered on the main body Ba of the bus bar B, and theassembling protrusions S holding the first and second end portions 11and 12 (for example, both edge portions of the first and second endportions 11 and 12) of the battery cells 10 may be arranged in a zigzagpattern. In addition, the branches Br and the assembling protrusions Smay be arranged in a zigzag pattern centered on the main body Ba of thebus bar B while being staggered. As such, the branches Br and theassembling protrusion S may all be brought into contact with the firstand second end portions 11 and 12 of the battery cells 10 at differentpositions of the first and second end portions 11 of the battery cells10. That is, the branches Br may be connected to the electrodes formedin the center portions of the first and second end portions 11 and 12 ofthe battery cells 10, and the assembling protrusions S may hold lateraledge portions of the first and second end portions 11 and 12 of thebattery cells 10.

FIG. 7 is a view illustrating a manner in which the first and secondholder plates 110 and 120 and the case 100, which are shown in FIG. 3,are coupled to each other and assembled together.

Referring to FIGS. 4 and 7, in an embodiment, skirt portions 113 may beformed on edges of the first and second holder plates 110 and 120 forassembling with the case 100. For example, the skirt portions 113 may beformed along the edges of the first and second holder plates 110 and 120in an inwardly bent shape. The skirt portions 113 formed on the edges ofthe first and second holder plates 110 and 120 may be inserted into thewell spaces W between the outer walls 101 and the inner walls 102 formedalong the edges of the case 100. For example, when the first and secondholder plates 110 and 120 are assembled to the case 100 while being slidinward along the case 100, the skirt portions 113 formed on the edges ofthe first and second holder plates 110 and 120 may be inserted into thewell spaces W between the outer walls 101 and the inner walls 102 formedon the edges of the case 100, and, thus, the first and second holderplates 110 and 120 may be coupled to the case 100. In an embodiment, theskirt portions 113 may be inserted into the well spaces W between theouter walls 101 and the inner walls 102 of the case 100, for example,while being brought into tight contact with the inner walls 102 tosurround the inner walls 102, rather than being brought into tightcontact with the outer walls 101, such that the first and second holderplates 110 and 120 on which the skirt portions 113 are formed may beassembled to the case 100 while surrounding the case 100.

In an embodiment, the first and second holder plates 110 and 120 havingthe skirt portions 113 may be assembled to the case 100 whilesurrounding the inner walls 102 of the case 100, and then the first andsecond holder plates 110 and 120 and the case 100 may be fastened toeach other using fastening members 6 (refer to FIG. 7). In anembodiment, for example, coupling holes 116 may be formed in the firstand second holder plates 110 and 120 to insert the fastening members 6(refer to FIG. 7) through the coupling holes 116, and coupling flangeportions 106 to be fastened may be formed on the case 100 to couple thefastening members 6 to the coupling flange portions 106. For example,the first and second holder plates 110 and 120 and the case 100 may becoupled to each other by inserting the fastening members 6 through thecoupling holes 116 of the first and second holder plates 110 and 120 andtightening the fastening members 6 in the coupling flange portions 106.The coupling holes 116 of the first and second holder plates 110 and 120may be formed at positions corresponding to the coupling flange portions106 of the case 100. For example, the coupling holes 116 may be formedin the first and second holder plates 110 and 120 at positions adjacentto the skirt portions 113 surrounding the inner walls 102 of the case100 in an intermittent manner along the edges of the first and secondholder plates 110 and 120 on which the skirt portions 113 are formed.The coupling flange portions 106 may be formed at positions adjacent tothe inner walls 102 of the case 100 in an intermittent manner along theinner walls 102 and may protrude toward the accommodation space G1.

In consideration of the coupling strength between the first and secondholder plates 110 and 120 and the case 100, a plurality of couplingholes 116 and a plurality of coupling flange portions 106 may be formedon the first and second holder plates 110 and 120 and the case 100 atcorresponding positions, and the coupling strength between the first andsecond holder plates 110 and 120 and the case 100 may be increased usingthe fastening members 6. For example, the coupling holes 116 may beformed at intermittent positions along the edges of the first and secondholder plates 110 and 120 on which the skirt portions 113 are formed,and the coupling flange portions 106 may be formed at intermittentpositions along the inner walls 102.

Referring to FIG. 5, in an embodiment, two neighboring rows of batterycells 10 may be arranged in a zigzag pattern in which battery cells 10are densely arranged in valleys between neighboring battery cells 10. Inan embodiment, battery cells 10 in one of the two neighboring rows maybe relatively shifted to the left such that areas for forming couplingholes 116 may be provided at right positions of the first and secondholder plates 110 and 120, and, similarly, battery cells 10 in the otherof the two neighboring rows may be relatively shifted to the right suchthat areas for forming coupling holes 116 may be provided at leftpositions of the first and second holder plates 110 and 120. As such,the first and second holder plates 110 and 120 may not requireadditional areas for forming the coupling holes 116. For reference, theleft positions or the right positions may be positions adjacent to oneside and the other side of the rows of the battery cells 10 which areparallel to the first and second short side portions 100S1 and 100S2 ofthe case 100. As described above, the coupling holes 116 of the firstand second holder plates 110 and 120 may be formed at alternating leftand right positions in the row direction of the battery cells 10, andthe coupling flange portions 106 (refer to FIG. 7) may be formed atpositions corresponding to the coupling holes 116.

FIG. 8 is a cutaway perspective view illustrating filling of the pottingresin F in the battery pack according to an embodiment; FIGS. 9A and 9Bare a cross-sectional view illustrating the battery pack shown in FIG. 8and an enlarged cross-sectional view illustrating a portion of thebattery pack shown in FIG. 9A, respectively; and FIG. 10 is an enlargedcross-sectional view illustrating a region “X” in FIG. 9A.

Referring to FIGS. 8 to 10, the potting resin F may be filled over thefirst and second holder plates 110 and 120. The potting resin F filledover the first and second holder plates 110 and 120 may securely sealthe accommodation space G1 of the cooling fluid formed between the firstand second holder plates 110 and 120. In an embodiment, the pottingresin F may include a silicone material having high moldability andsealing properties. However, the potting resin F of the presentdisclosure is not limited thereto and may include any other suitablematerial. In an embodiment, the potting resin F may be surrounded by theouter walls 101 forming the edges of the case 100 such that the pottingresin F may be formed on the first and second holder plates 110 and 120to a certain height without overflow to the outside. That is, the outerwalls 101 of the case 100 may define filling spaces G2 for the pottingresin F. In an embodiment, the potting resin F is formed on the firstand second holder plates 110 and 120, and a height HF (refer to FIGS. 9Aand 9B) of the potting resin F may be greater than at least the heightH15 between the first and second holder plates 110 and 120. Here, theheight HF of the potting resin F is a height from a portion of thepotting resin F formed on the first holder plate 110 to a portion of thepotting resin F formed on the second holder plate 120, that is, a heightbetween the portions of the potting resin F formed on the first andsecond holder plates 110 and 120. In other words, the height HF of thepotting resin F does not refer to only the thicknesses of layers of thepotting resin F formed on the first and second holder plates 110 and120, but may refer to the sum of the thicknesses of the layers of thepotting resin F formed on the first and second holder plates 110 and120, the thicknesses t of the first and second holder plates 110 and120, and the height HG of the accommodation space G1 formed between thefirst and second holder plates 110 and 120.

In an embodiment, the cooling fluid for cooling the battery cells 10 maybe securely contained in the accommodation space G1 between the firstand second holder plates 110 and 120, and the potting resin F may befilled over the first and second holder plates 110 and 120 to prevent orsubstantially prevent leakage of the cooling fluid. In this case, theheight H10 of the case 100 (for example, the height of the outer walls101) may function as a dam such that the potting resin F may be formedon the first and second holder plates 110 and 120 to a certain height(e.g., a predetermined height) without overflow to the outside. In anembodiment, the height HF of the potting resin F may be lower than theheight H10 of the case 100. The height HF of the potting resin F may begreater than the height H15 between the first and second holder plates110 and 120 on which the potting resin F is formed, but may be less thanthe height H10 of the case 100 functioning as a dam for the pottingresin F, that is, H15<HF<H10.

In an embodiment, the potting resin F may be formed to a height at whichthe first and second end portions 11 and 12 of the battery cells 10 arecompletely covered with the potting resin F. In this case, the height HFof the potting resin F may be greater than the height HC of the batterycells 10 (HF>HC). For example, the potting resin F may cover the firstand second end portions 11 and 12 of the battery cells 10, and couplingportions Cp between the first and second end portions 11 and 12 of thebattery cells 10 and the bus bars B (for example, the branches Br of thebus bars B). The coupling portions Cp may include welded portionsbetween the first and second end portions 11 and 12 of the battery cells10 and the branches Br of the bus bars B. In this manner, since thepotting resin F covers the coupling portions Cp between the first andsecond end portions 11 and 12 of the battery cells 10 and the bus bars B(for example, the branches Br of the bus bars B), the coupling portionsCp may be protected from harmful environmental factors which may causecorrosion, oxidation, or galvanic corrosion of the coupling portions Cp.In an embodiment, the height HF of the potting resin F may be greaterthan the height HC of the battery cells 10, but less than the height H10of the case 100 functioning as a dam for the potting resin F, that is,HC<HF<H10).

Referring to FIG. 8, in an embodiment, the potting resin F may cover thecoupling portions Cp between the first and second end portions 11 and 12of the battery cells 10 and the branches Br of the bus bars B, and thebranches Br and the main bodies Ba of the bus bars B as well. Althoughnot shown, in another embodiment, the potting resin F may cover thecoupling portions Cp between the first and second end portions 11 and 12of the battery cells 10 and the branches Br of the bus bars B, but maynot cover the main bodies Ba of the bus bars B. In an embodiment, themain bodies Ba of the bus bars B may have a height difference in anoutward (for example, upward) direction from the first and second endportions 11 and 12 of the battery cells 10 because the branches Br arebent in a stepped shape in inward (for example, downward) directionsfrom the main bodies Ba (at bent portions Bc) and connected to the firstand second end portions 11 and 12 of the battery cells 10. In anembodiment, the potting resin F may cover the coupling portions Cpbetween the battery cells 10 and the branches Br which requirerelatively high protection, but may not cover the main bodies Ba of thebus bars B, such an amount of the potting resin F may be reduced.

Referring to FIGS. 9A and 9B, since the outer walls 101 of the case 100define the filling spaces G2 in which the potting resin F is filled andserve as a dam for containing the potting resin F, the height of theouter walls 101 (for example, the height H10 of the case 100) may begreater than the height of the inner walls 102. In an embodiment, theouter walls 101 and the inner walls 102 may be connected through thebottom surfaces 103 formed between the outer walls 101 and the innerwalls 102, and may protrude to different heights from the bottomsurfaces 103. In an embodiment, the inner walls 102 form the well spacesW connected to the filling spaces G2, and the height of the inner walls102 may be less than the height of the outer walls 101.

In an embodiment, the height HC of the battery cells 10 may be greaterthan the height of the inner walls 102 but less than the height of theouter walls 101. The inner walls 102 may regulate the height H15 betweenthe first and second holder plates 110 and 120, and the heights of thefirst and second holder plates 110 and 120 may be determined as thefirst and second holder plates 110 and 120 are brought into contact withthe inner walls 102. As described above, the first and second endportions 11 and 12 of the battery cells 10 may be away from the firstand second holder plates 110 and 120 and may be exposed from theaccommodation space G1 of the cooling fluid, and the height H15 betweenthe first and second holder plates 110 and 120 may be less than theheight HC of the battery cells 10. In an embodiment, the height of theinner walls 102 regulating the height H15 between the first and secondholder plates 110 and 120 may be less than the height HC of the batterycells 10. In addition, the height H10 of the case 100, that is, theheight of the outer walls 101 may be greater than at least the height HCof the battery cells 10 such that the battery cells 10 may be completelyaccommodated in the case 100. As described above, the potting resin Fmay be filled over the first and second holder plates 110 and 120 to aheight at which the first and second end portions 11 and 12 of thebattery cells 10 exposed through the first and second holder plates 110and 120 are covered with the potting resin F, and, thus, the height H10of the case 100, that is, the height of the outer walls 101 functioningas a dam for containing the potting resin F may be greater than at leastthe height HC of the battery cells 10 such that the outer walls 101 mayhave an additional height remaining even after covering the pottingresin F.

Referring to FIG. 10, the well spaces W may be formed along the edges ofthe case 100 to hermetically seal the accommodation space G1 of thecooling fluid. As described above, the potting resin F may be formed onthe first and second holder plates 110 and 120 to hermetically seal theaccommodation space G1 of the cooling fluid which is formed between thefirst and second holder plates 110 and 120. In this case, the pottingresin F may fill the filling spaces G2 above the first and second holderplates 110 and 120 and also the well spaces W formed along the edges ofthe case 100, thereby preventing or substantially preventing leakage ofthe cooling fluid through the edges of the case 100.

In an embodiment, the well spaces W may include concave spaces definedby the outer walls 101 and the inner walls 102 of the case 100, and thebottom surfaces 103 connecting the outer walls 101 and the inner walls102 to each other. For example, the well spaces W may be defined by theinner walls 102 and the skirt portions 113 of the first and secondholder plates 110 and 120 surrounding the inner walls 102, and mayinclude spaces between the inner walls 102 and the outer walls 101 andspaces between the outer walls 101 and the skirt portions 113surrounding the inner walls 102.

The well spaces W may be connected to the filling spaces G2 formed onthe first and second holder plates 110 and 120 such that all the wellspaces W and the filling spaces G2 may be filled with the potting resinF. In an embodiment, for example, the potting resin F may becontinuously formed in the well spaces W and the filling spaces G2without disconnection or separation. The well spaces W and the fillingspaces G2 may be connected to each other in a stepped manner in thewidth direction thereof. For example, the well spaces W, which have arelatively small width between the outer walls 101 and the inner walls102, may be connected to the filling spaces G2, which have a relativelylarge width and are surrounded by the outer walls 101 at a height awayfrom the inner walls 102, in a stepped manner in the width directionthereof.

In an embodiment, the boundaries defining the well spaces W may bebypassing boundaries which bend along the inner walls 102, the bottomsurfaces 103, and the outer walls 101, and due to the well spaces W (orthe potting resin F filled in the well spaces W) having the bypassingboundaries in a bent shape, leakage of the cooling fluid contained inthe accommodation space G1 may be effectively prevented. In anembodiment, for example, to prevent or substantially prevent the coolingfluid from leaking from the accommodation space G1 along the boundariesof the well spaces W (or the potting resin F filled in the well spacesW), the boundaries of the well spaces (or the potting resin F filled inthe well spaces W) are formed as bypassing boundaries having a bentshape to increase a path through which the cooling fluid flows andeffectively prevent leakage of the cooling fluid.

FIG. 11 is a cutaway perspective view illustrating filling of a pottingresin in the battery pack according to another embodiment; FIGS. 12A and12B are a cross-sectional view illustrating the battery pack shown inFIG. 11 and an enlarged cross-sectional view illustrating a portion ofthe battery pack shown in FIG. 12A, respectively; and FIG. 13 is apartially exploded perspective view illustrating a cover coupled to thebattery pack shown in FIG. 11.

Referring to FIGS. 11, 12A, and 12B, in another embodiment, a pottingresin F may be formed to a certain height (e.g., a predetermined height)from the first and second holder plates 110 and 120, and may not coverthe first and second end portions 11 and 12 of the battery cells 10.That is, the height HF of the potting resin F may be less than theheight HC of the battery cells 10 (HF<HC). In an embodiment, a vent V(refer to FIG. 11) may be formed in at least one of the first and secondend portions 11 and 12 of each of the battery cells 10, and the pottingresin F may not cover the first and second end portions 11 and 12 of thebattery cells 10 so as not to hinder or block the release of pressurefrom the insides of the battery cells 10 through the vents V. In anembodiment, the vents V (refer to FIG. 11) may be formed along the edgesof the first end portions 11 or the second end portions 12 of thebattery cells 10. In an embodiment, two rows of battery cells 10connected through a bus bar B may be arranged upside down relative toeach other in the height direction of the battery cells 10 such that thepositive and negative polarities of the two rows of battery cells 10 maybe reversed, and thus the vents V (refer to FIG. 11) may be formed inthe first end portions 11 or the second end portions 12 according to thepositions of the battery cells 10. In an embodiment, the height HF(refer to FIGS. 12A and 12B) of the potting resin F may be greater thanthe height H15 between the first and second holder plates 110 and 120 onwhich the potting resin F is formed, but may be less than the height HCof the battery cells 10, that is, H15<HF<HC).

As described above, since the first and second end portions 11 and 12 ofthe battery cells 10 are exposed from the potting resin F, the couplingportions Cp between the bus bars B and the first and second end portions11 and 12 of the battery cells 10 may be exposed. However, the couplingportions Cp may be protected from environmental factors by first andsecond covers 51 and 52 which cover the case 100 as shown in FIG. 13.That is, the first and second covers 51 and 52 may be assembled to coverthe case 100 in mutually-facing directions with the case 100therebetween, and, thus, the coupling portions Cp between the bus bars Band the first and second end portions 11 and 12 may be protected withoutbeing exposed to the outside.

FIGS. 14 and 15 are an exploded perspective view and a plan view,respectively, which illustrate a partition wall structure of a batterypack according to an embodiment.

Referring to FIG. 14, the accommodation space G1 may be formed betweenthe first and second holder plates 110 and 120 that are assembled toface each other along the case 100. In this case, the accommodatingspace G1 may accommodate a flow of a cooling fluid for cooling thebattery cells 10, and a partition wall 150 may extend across theaccommodating space G1 of the case 100 to divide the accommodation spaceG1 into an upstream portion G11 and a downstream portion G12. In anembodiment, for example, the partition wall 150 may be integrally formedwith the case 100.

The upstream portion G11 may be connected to the inlet I of the coolingfluid, such that the cooling fluid may flow into the upstream portionG11 at a relatively low temperature, and the downstream portion G12 maybe connected to the outlet O of the cooling fluid, such that the coolingfluid may flow outward from the downstream portion G12 at a relativelyhigh temperature. The inlet I and the outlet O of the cooling fluid maybe formed at an end side in the extending direction of the partitionwall 150, and a communication portion CN may be provided at the otherend side in the extending direction of the partition wall 150 to connectthe upstream portion G11 and the downstream portion G12 to each other.In an embodiment, for example, the extending direction of the partitionwall 150 may be parallel to the long side portions 100L.

The communication portion CN may connect the upstream portion G11 andthe downstream portion G12 to each other, and, thus, the cooling fluidflowing in the upstream portion G11 in a direction from the inlet I ofthe end side toward the other end side may be reversed, that is, turnedin a U-shape, and may flow in the downstream portion G12 in a directionfrom the other end side toward the outlet O of the end side.

The inlet I and the outlet O may be formed at the end side in theextending direction of the partition wall 150, for example, at the firstshort side portion 100S1 of the case 100. In an embodiment, as describedabove, the inlet I and the outlet O are formed together in the firstshort side portion 100S1 of the case 100, and, for example, since theinlet I and the outlet O are not respectively formed in the first andsecond short side portions 100S1 and 100S2 that are opposite each other,but are formed together in the first short side portion 100S1, fluidconnection to the case 100 may be easily made. For example, the case 100may include: the pair of long side portions 100L parallel to theextending direction of the partition wall 150; and the first and secondshort side portions 100S1 and 100S2 connecting the pair of long sideportions 100L to each other, wherein the inlet I and the outlet O may beformed together in the first short side portion 100S1 rather than beingrespectively formed in the first and second short side portions 10051and 100S2.

In an embodiment, the inlet I and the outlet O are formed in the firstshort side portion 10051 of the case 100, and the flow of the coolingfluid is directed from the inlet I toward the outlet O using thepartition wall 150 provided in the case 100 by reversing the flow of thecooling fluid in a U-turn form at the second short side portion 10052,such that a relatively large flow resistance may be applied to the flowof the cooling fluid to completely or nearly completely fill the inside(accommodation space G1) of the case 100 with the cooling fluid.

In an embodiment, one inlet I and one outlet O may be formed together inthe first short side portion 100S1 of the case 100 as a pair. However,embodiments of the present disclosure are not limited thereto. Inanother embodiment, inlets I and outlets O may be respectively formed inthe first and second short side portions 10051 and 10052 of the case100, and a number of inlets I and a number of outlets O may be equal toeach other or different from each other, and may each be at least two.For example, referring to FIG. 14, one partition wall 150 is provided inthe case 100 to divide the accommodation space G1 into two portions: theupstream portion G11 connected to the inlet I, and the downstreamportion G12 connected to the outlet O. However, in another embodiment,at least two partition walls 150 may be provided to divide theaccommodation space G1 into a plurality of portions, and two or moreinlets I and outlets O may be formed such that an inlet I or an outlet Omay be provided in each of the portions. In an embodiment, the number ofinlets I and the number of outlets O may be different from each other.For example, the numbers of inlets I and outlets O may be adjusted tocontrol the flow resistance or flow rate of the cooling fluid, and tocontrol the flow rate of the cooling fluid by considering the efficiencyof cooling according to driving power to prevent or substantiallyprevent the absence of cooling in a local area.

Referring to FIG. 15, in an embodiment, the partition wall 150 may beprovided such that the number of battery cells 10 or cell holes 115defining the assembling positions of battery cells 10 in the upstreamportion G11 may be equivalent to the number of battery cells 10 or cellholes 115 in the downstream portion G12 for distributing the burden ofheat dissipation uniformly or substantially uniformly to the coolingfluid in the upstream portion G11 and the downstream portion G12. In anembodiment, for example, the battery cells 10 (or the cell holes 115)may be arranged in eight rows in the extending direction of thepartition wall 150, and the partition wall 150 may divide the eight rowsinto four rows in the upstream portion G11 and four rows in thedownstream portion G12. In an embodiment, the number of battery cells 10in the upstream portion G11 and the number of battery cells 10 in thedownstream portion G12 may be equivalent to each other to distribute theheat-dissipating burden of the cooling fluid uniformly or substantiallyuniformly to the upstream portion G11 and the downstream portion G12.

When the partition wall 150 extends between first and second rows L1 andL2 neighboring each other, the first and second rows L1 and L2 may bearranged adjacent to each other such that cell holes 115 (or batterycells 10) of the first row L1 may be placed between cell holes 115 (orbattery cells 10) of the second row L2, and, in an embodiment, thepartition wall 150 may extend in a serpentine shape between the firstand second rows L1 and L2. For example, the partition wall 150 mayextend in a zigzag pattern along outer surfaces of the battery cells 10of the first and second rows L1 and L2, and, thus, the partition wall150 may include a plurality of bent portions.

Referring to FIGS. 14 and 15, in an embodiment, the partition wall 150may include: a wall body portion 155 extending across the accommodationspace G1; and first and second coupling portions 151 and 152 coupled tothe first and second holder plates 110 and 120 at intermittent positionsin a direction from an end side to the other end side. The first andsecond coupling portions 151 and 152 may be coupled to clearanceportions 118 of the first and second holder plates 110 and 120,respectively.

In an embodiment, the partition wall 150 may extend along the clearanceportions 118 between the cell ribs R, and the first and second couplingportions 151 and 152 of the partition wall 150 may be brought intocontact with and welded to the clearance portions 118 of the first andsecond holder plates 110 and 120. The first and second coupling portions151 and 152 may protrude with a large width in the thickness directionof the wall body portion 155 and may form a wide contact area with theclearance portions 118 of the first and second holder plates 110 and120. In an embodiment, the first and second coupling portions 151 and152 may be connected to each other while extending in the heightdirection of the wall body portion 155.

In an embodiment, each of the clearance portions 118 of the first andsecond holder plates 110 and 120 may be provided by an extra space amongfour neighboring cell ribs R having adjacent outer circumferences. Forexample, the cell ribs R may be densely arranged in such a manner thatthe outer circumferences of every four cell ribs R which surround theouter circumferences of densely arranged battery cells 10 may beadjacent to each other. In addition, the clearance portions 118 eachprovided as an extra space among four cell ribs R may provide couplingpositions for fixing the position of the partition wall 150 in the case100.

Referring to FIG. 14, the wall body portion 155 of the partition wall150 may have first and second heights h1 and h2 along the partition wall150. The wall body portion 155 of the partition wall 150 may have thefirst height h1 over most of the length of the wall body portion 155from the end side (first short side portion 10051) in which the inlet Iand the outlet O are formed, and may separate the upstream portion G11and the downstream portion G12 from each other at a position between thefirst and second holder plates 110 and 120. The wall body portion 155 ofthe partition wall 150 may have the second height h2 at the other endside (second short side portion 10052) which is less than the firstheight h1 at the end side (first short side portion 10051) so as to formthe communication portion CN connecting the upstream portion G11 and thedownstream portion G12 to each other at the other end side (second shortside portion 10052) which is opposite the end side in which the inlet Iand the outlet O are formed, and the communication portion CN maycorrespond to the difference between the first height h1 and the secondheight h2. That is, the wall body portion 155 of the partition wall 150may be stepped from the first height h1 of the end side to the secondheight h2 of the other end side, and the communication portion CN maycorrespond to the difference between the first height h1 and the secondheight h2.

In an embodiment, the portion having the second height h2 may correspondto a center region of the portion having the first height h1, and, thus,there may be an upper height difference and a lower height differencebetween the portion having the second height h2 and the portion havingthe first height h1. In this case, the communication portion CN mayinclude a first communication portion CN1 corresponding to the upperheight difference adjacent to the first holder plate 110 and a secondcommunication portion CN2 corresponding to the lower height differenceadjacent to the second holder plate 120, and the cooling fluid maysmoothly flow between the upstream portion G11 and the downstreamportion G12 through the first and second communication portions CN1 andCN2 which are opposite to each other in the height direction of thepartition wall 150. For example, the first communication portion CN1 mayform a flow of the cooling fluid which makes contact with portionsrelatively adjacent to the first end portions 11 of the battery cells10, and the second communication portion CN2 may form a flow of thecooling fluid which makes contact with portions relatively adjacent tothe second end portions 12 of the battery cells 10. In an embodiment,due to the first and second communication portions CN1 and CN2, thecooling fluid may flow along portions adjacent to the first and secondend portions 11 and 12 at which heating mainly occurs.

As described above, according to the one or more embodiments, thecooling fluid may flow in the accommodation space of the battery cells10 and may directly make contact with the surfaces of the battery cells10, thereby efficiently dissipating heat from the battery cells 10 bydirect convective heat transfer.

In addition, according to the embodiments, the cooling fluid may beinsulated from the electrodes of the battery cells 10 to prevent orsubstantially prevent electrical interference therebetween.

It is to be understood that embodiments described herein should beconsidered in a descriptive sense and not for purposes of limitation.Descriptions of features or aspects within each embodiment shouldtypically be considered as available for other similar features oraspects in other embodiments. While one or more embodiments have beendescribed with reference to the figures, it will be understood by thoseof ordinary skill in the art that various changes in form and detailsmay be made therein without departing from the spirit and scope as setforth in the following claims.

What is claimed is:
 1. A battery pack comprising: battery cells, eachcomprising end portions in a height direction of the battery cells; acase accommodating the battery cells and a cooling fluid to cool thebattery cells; and a first holder plate and a second holder plate thatare coupled to the case to face each other along the case such that theend portions of the battery cells are insertable through the first andsecond holder plates, an accommodation space being defined between thefirst and second holder plates to accommodate the cooling fluid, whereinthe case, the battery cells, and the first and second holder plates haveheights in the height direction of the battery cells that satisfy thefollowing condition: a height between the first and second holder plates<a height of the battery cells <a height of the case, and the casecomprises a hollow member which is open in the height direction.
 2. Thebattery pack of claim 1, wherein assembling protrusions protrude outwardfrom the first and second holder plates away from the accommodationspace to hold the end portions of the battery cells.
 3. The battery packof claim 2, wherein the first and second holder plates comprise cellholes, and the battery cells are insertable into the cell holes, and theassembling protrusions are arranged along rows of the cell holes to holdthe end portions of the battery cells neighboring each other in a statein which the assembling protrusions are at positions between the cellholes neighboring each other.
 4. The battery pack of claim 2, furthercomprising a bus bar electrically connecting the battery cells to eachother, wherein some of the assembling protrusions comprise firstassembling protrusions that hold the end portions of the battery cellsand do not physically interfere with the bus bar, and others of theassembling protrusions comprise second assembling protrusions that holdthe end portions of the battery cells and the bus bar.
 5. The batterypack of claim 4, wherein the bus bar comprises a main body extendingalong rows of the battery cells and branches branching from the mainbody toward the battery cells, and the branches and the assemblingprotrusions are staggered in a zigzag pattern centered on the main body.6. The battery pack of claim 5, wherein the main body extends in a rowdirection of the battery cells between outermost branches located onends of the main body, and the second assembling protrusions areadjacent to inner sides of the outermost branches.
 7. The battery packof claim 4, wherein the first and second assembling protrusions comprisefirst protrusion portions protruding toward the end portions of thebattery cells, and the second assembling protrusions further comprisesecond protrusion portions protruding toward the bus bar.
 8. The batterypack of claim 7, wherein the first protrusion portions are on oppositesides of the second assembling protrusions, and the second protrusionportions are on sides of the second assembling protrusions between theopposite sides.
 9. The battery pack of claim 8, wherein the first andsecond protrusion portions have a height difference in the heightdirection.
 10. The battery pack of claim 1, wherein cell ribs protrudeinward from the first and second holder plates toward the accommodationspace and are arranged around outer circumferential surfaces of thebattery cells.
 11. The battery pack of claim 10, wherein gaps aredefined between the outer circumferential surfaces of the battery cellsand the cell ribs.
 12. The battery pack of claim 1, wherein the casecomprises outer walls and inner walls extending in parallel to eachother along edges of the case which surround the accommodation space.13. The battery pack of claim 12, wherein the battery cells, the outerwalls, and the inner walls have heights that satisfy the followingcondition: a height of the inner walls <the height of the battery cells<a height of the outer walls.
 14. The battery pack of claim 12, whereinwell spaces are defined between the outer walls and the inner wallsalong the edges of the case.
 15. The battery pack of claim 14, furthercomprising a potting resin on the first and second holder plates, thepotting resin being continuously arranged in the well spaces.
 16. Thebattery pack of claim 14, wherein skirt portions are bent inward fromthe first and second holder plates toward the well spaces and insertedinto the well spaces.
 17. The battery pack of claim 16, wherein theskirt portions are bent and extend from the first and second holderplates and are arranged around the inner walls.
 18. The battery pack ofclaim 1, further comprising a potting resin on the first and secondholder plates.
 19. The battery pack of claim 18, wherein the pottingresin on the first and second holder plates has a height in the heightdirection that satisfies the condition: the height of the battery cells<a height of the potting resin <the height of the case.
 20. The batterypack of claim 19, further comprising a bus bar electrically connectingthe battery cells to each other, wherein the potting resin coverscoupling portions between the bus bar and the battery cells.
 21. Thebattery pack of claim 18, wherein the potting resin on the first andsecond holder plates has a height in the height direction that satisfiesthe following condition: the height between the first and second holderplates <the height of the potting resin <the height of the batterycells.
 22. The battery pack of claim 21, wherein the potting resinexposes vents in the end portions of the battery cells.